From 5d753610277862fd8050901f38b6571b9500cdb6 Mon Sep 17 00:00:00 2001 From: Mel Gorman Date: Wed, 10 Jun 2015 21:02:04 -0400 Subject: [PATCH] net, swap: Remove a warning and clarify why sk_mem_reclaim is required when deactivating swap Jeff Layton reported the following; [ 74.232485] ------------[ cut here ]------------ [ 74.233354] WARNING: CPU: 2 PID: 754 at net/core/sock.c:364 sk_clear_memalloc+0x51/0x80() [ 74.234790] Modules linked in: cts rpcsec_gss_krb5 nfsv4 dns_resolver nfs fscache xfs libcrc32c snd_hda_codec_generic snd_hda_intel snd_hda_controller snd_hda_codec snd_hda_core snd_hwdep snd_seq snd_seq_device nfsd snd_pcm snd_timer snd e1000 ppdev parport_pc joydev parport pvpanic soundcore floppy serio_raw i2c_piix4 pcspkr nfs_acl lockd virtio_balloon acpi_cpufreq auth_rpcgss grace sunrpc qxl drm_kms_helper ttm drm virtio_console virtio_blk virtio_pci ata_generic virtio_ring pata_acpi virtio [ 74.243599] CPU: 2 PID: 754 Comm: swapoff Not tainted 4.1.0-rc6+ #5 [ 74.244635] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 [ 74.245546] 0000000000000000 0000000079e69e31 ffff8800d066bde8 ffffffff8179263d [ 74.246786] 0000000000000000 0000000000000000 ffff8800d066be28 ffffffff8109e6fa [ 74.248175] 0000000000000000 ffff880118d48000 ffff8800d58f5c08 ffff880036e380a8 [ 74.249483] Call Trace: [ 74.249872] [] dump_stack+0x45/0x57 [ 74.250703] [] warn_slowpath_common+0x8a/0xc0 [ 74.251655] [] warn_slowpath_null+0x1a/0x20 [ 74.252585] [] sk_clear_memalloc+0x51/0x80 [ 74.253519] [] xs_disable_swap+0x42/0x80 [sunrpc] [ 74.254537] [] rpc_clnt_swap_deactivate+0x7e/0xc0 [sunrpc] [ 74.255610] [] nfs_swap_deactivate+0x27/0x30 [nfs] [ 74.256582] [] destroy_swap_extents+0x74/0x80 [ 74.257496] [] SyS_swapoff+0x222/0x5c0 [ 74.258318] [] ? syscall_trace_leave+0xc7/0x140 [ 74.259253] [] system_call_fastpath+0x12/0x71 [ 74.260158] ---[ end trace 2530722966429f10 ]--- The warning in question was unnecessary but with Jeff's series the rules are also clearer. This patch removes the warning and updates the comment to explain why sk_mem_reclaim() may still be called. [jlayton: remove if (sk->sk_forward_alloc) conditional. As Leon points out that it's not needed.] Cc: Leon Romanovsky Signed-off-by: Mel Gorman Signed-off-by: Jeff Layton Signed-off-by: David S. Miller --- net/core/sock.c | 13 +++++-------- 1 file changed, 5 insertions(+), 8 deletions(-) diff --git a/net/core/sock.c b/net/core/sock.c index 292f42228bfb..469d6039c7f5 100644 --- a/net/core/sock.c +++ b/net/core/sock.c @@ -354,15 +354,12 @@ void sk_clear_memalloc(struct sock *sk) /* * SOCK_MEMALLOC is allowed to ignore rmem limits to ensure forward - * progress of swapping. However, if SOCK_MEMALLOC is cleared while - * it has rmem allocations there is a risk that the user of the - * socket cannot make forward progress due to exceeding the rmem - * limits. By rights, sk_clear_memalloc() should only be called - * on sockets being torn down but warn and reset the accounting if - * that assumption breaks. + * progress of swapping. SOCK_MEMALLOC may be cleared while + * it has rmem allocations due to the last swapfile being deactivated + * but there is a risk that the socket is unusable due to exceeding + * the rmem limits. Reclaim the reserves and obey rmem limits again. */ - if (WARN_ON(sk->sk_forward_alloc)) - sk_mem_reclaim(sk); + sk_mem_reclaim(sk); } EXPORT_SYMBOL_GPL(sk_clear_memalloc); -- GitLab